Gasifying an extraneous liquefied gas and simultaneously liquefying another gas



J. L. SCHLITT GASIFYING AN EXTRANEOUS LIQUEFIED GAS AND SIMULTANEOUSLY LIQUEFYING ANOTHER GAS Filed April 30, 1952 ATTORNEY l atented Aug. 3, 1954 GASIFYING AN EXTRANEOUS LIQUEFIED GAS AND SIMULTANEOUSLY LIQUEFYING ANOTHER GAS Joseph L. Schlitt, deceased, late of Darien, Conn., by Emily C. Schlitt, executrix, Darien, Conn., assignor to Air Reduction Company, Incorporated, New York, N. Y., a corporation of New York Application April 30, 1952, Serial No. 285,173

11 Claims. 1

This invention relates to the liquefaction of gases and more particularly to a method and means for the production of liquefied air or other gas and simultaneously for the gasification of an extraneous liquefied gas.

It is an object of this invention to provide a simple, economical process and apparatus for utilizing the refrigerative capacity of an extraneous body of liquefied gas in the liquefaction of a quantity or a gas, such as air.

It is a further object of this invention to provide a simplified process and apparatus for the production of liquefied air by using the refrigerative eiiect of an extraneous body of liquefied gas in which process and apparatus the produced liquefied air product is freed from impurities, such as acetylene.

In recent years in this country, the demands for oxygen gas for various industrial uses have increased significantly; and, as a consequence thereof, it has become common practice to transport liquefied oxygen, which is produced in a large centrally-located plant, to the place of use in order to achieve low transportion and storage costs.

Since oxygen is generally utilized as a gas, as in gas welding for instance, it is necessary that any liquefied oxygen at the site of use be converted to a gas. The usual practice at the site of large steady consumers is to vaporize the stored liquefied oxygen by means of electricallyproduced or steam-produced heat. This procedure, in effect, wastes the heat absorbing capacity of the liquefied gas since it is not put to beneficial use and actually requires heat energy to offset the cold. It is to be noted that the heat absorbing capacity, or refrigerative capacity, of the liquefied gas was in effect created by electrical power since the liquefaction and separation plant is basically dependent on electricallypowered compressors. Obviously any process which can efiiciently utilize this refrigerative capacity of the liquefied gas would be highly desirable and would result in a greater overall efficiency by obtaining a more complete energy return. It is to be noted that any efficient liquefaction process which utilizes the refrigerative capacity of liquefied oxygen, and hence is properly arranged to gasify the liquefied oxygen, in addition eifects a further economy since no external, costly-to-produce heat is required to gasify the liquefied oxygen as has heretofore often been used.

Also in recent years the demand for liquefied air has increased since its industrial uses, such as metal shrink fitting, have become more widespread. Normally the equipment which is necessary for the conventional production of liquefied air involves a considerable capital investment and. requires an appreciable degree of control in operation. It can be appreciated that an efficient process for the liquefaction of air which reduces capital costs and the degree of operational control is also highly desirable.

The instant invention provides a means for obtaining the aforementioned desirable results, and so avoids the loss of the refrigerative capacity of a liquefied gas, the usual costs of vaporizing a liquefied gas, and some of the operational and capital expenses of a conventional liquefied air plant. This is accomplished by providing a simplified, economical process and apparatus for liquefying air, in which process and apparatus the refrigerative capacity of an extraneous liquefied gas, such as stored oxygen, is utilized, and simultaneously the extraneous liquefied gas is gasified and pressurized for use. Thus a single consumer, or adjacent users, of gasified oxygen and liquefied air can be economically provided with his, or their, needs.

The instant invention, in addition, provides a specific means and method for removing higher boiling-point impurities such as acetylene from air by scrubbing with a liquefied gas which is broadly similar to the method disclosed in Patent No. 2,502,282 issued to the inventor of the instant invention on March 28, 1950.

The accomplishment of the aforementioned objects and the advantages and features of the invention can be better appreciated and understood by reference to the following description and the accompanying drawing which diagrammatically shows apparatus suitable for practicing the method of the instant invention. On the drawing the flow of fluid is indicated by arrows.

In accordance with the present invention, an atmospheric air stream in pipe I!) enters the primary compressor l2 and is compressed therein to less than 30 p. s. i. g. The low-pressurized impure air stream then passes in pipe i l to coil it of the water-cooled aftercooler it. In aftercooler IS the air is cooled, removing the heaf'bf compression, to about room temperature by the cooling water which passes through it. From the aftercooler I8 the compressed and cooled air is delivered through conduit 20 to heat exchanger 2i which has passages 22, 24, 26. Exchanger 2! is shown with the three parallel passages 22, 24, and 26 in the interests of clarity; but, in practice, would be a reversing heat exchanger or suitable regenerators which are well known in the art and serve to remove the carbon dioxide and water vapor from the air. However, if the air is purified previously by chemical means, exchanger 2! may be the usual tubular type. In the schematic apparatus shown, the air stream passes through the center passage 24 and is cooled to substantially its liquefaction temperature by indirect heat exchange with colder counter-flowing fluids in passages 22, 26 of exchanger 2!. These fluids are process streams which are derived in a manner to be described hereinafter.

From exchanger 2| the cold gaseous air passes to scrubber 28 by means of pipe as which enters the bottom portion of the scrubber below the lower level of the mixing structure within the scrubber. The mixing structure shown in the drawing is the well-known tray-bubble-cap construction and is comprised of liquid trays and bubble caps for gases which assure an intimate contact between the upwardly flowing gaseous air and the downwardly flowing purified liquid air which is introduced through pipe 32 at the top of the scrubber 28. The intimate contact of gaseous air, containing higher boilingpoint impurities such as acetylene, and purified liquid air causes the impurities to be taken up and retained in the liquid. In addition the scrubbing or washing liquid removes any entrained residual carbon dioxide and water ice which passes from exchanger 2| through pipe 3! The liquid, containing the impurities, collects in the bottom of the scrubber and is withdrawn through pipe 3 In pipe 34 the flow of liquid is controlled by valve 36 and the liquid then fiows through passage 26 of heat exchanger 2l, absorbing heat and thus cooling the incoming low-pressurized air fiowing in passage 24 of exchanger 21. The absorbed heat vaporizes the liquid and the impurities and these vapors, being at about room temperature, are then discarded through pipe 38, which connects to passage 28 of heat exchanger 2 l. The amount of discarded impurities-containing liquid is small, being about 1% of the total of the produced liquefied air, and is economically utilized as just mentioned in the heat exchanger 2 i. In this manner the collection of small but hazardous amounts of acetylene or other higher boilingpoint combustibles in the apparatus is avoided.

The liquid for the scrubbing which enters scrubber 28 through pipe 32 is liquefied air which has been previously purified in the scrubber and then liquefied in the process in a manner which will be subsequently described.

It is to be noted that some of the scrubbing liquid will be vaporized and that the scrubbing cools the incoming gaseous air.

The scrubbed gaseous air or washed air and the vaporized portion of scrubbing liquid are Withdrawn from the top of the scrubber through pipe 48. This scrubbed eiiluent or purified gas stream is then divided at the T-ioint 4|. A small minor fraction or flow of the effluent passes through valve 2 for a purpose which will subsequently be described. The majority of the air flow or major fraction in pipe 41] is returned through pipe 44 to passage 22 of the heat exchanger 2! where it cools the incoming air and is consequently warmed. From heat exchanger 2! the warm major fraction is passed through pipe 46 to the secondary compressor 48 and its water-cooled aftercooler 51}. The air leaving cooler 58 in conduit 52 is at about atmospheric temperature and usually about 300 p. s. i. g. The air then passes to the air liquefier 54 wherein the relatively warm air is liquefied in passage 58 by indirect heat exchange with a quantity of an extraneous liquefied gas (such as liquefied oxygen) which is gasified or evaporated and pressurized in passage 60 of air liquefier 54. In this manner, the heat for gasification and pressurizing of oxygen is in effeet the heat released during the condensation of the air. Thus, liquid oxygen is converted to oxygen in the gas phase and gaseous air is changed to its liquid phase.

From passage 58 of air liquefier 54 the liquefied air flows through pipe 62 to subcooler 64 Where the liquefied air is subcooled in passage 66 by cold vapors flowing through passage 68. The subcooled liquefied air leaves subcooler 66 through pipe '10 which contains an expansion valve 12. The liquefied air is expanded or thrcttled by means of valve 12 to a lower pressure of the order'of 30 p. s. i. g. and is thus cooled by the well-known Joule-Thomson effect to about a temperature of -180 C. The expansion produces some vapors (mostly nitrogen) which flow along with the liquid in conduit 10 to liquid air receiver 74 in which the residual liquid is collected. These cold vapors flow out of the top of the receiver M by means of conduit t6 and are recirculated and used, by moving counter-currently through passage 58, to subcool, as mentioned above, the liquefied air in passage 66 of air subcooler 64. After being used for subcooling, these vapors, via pipe 18, then join the minor portion of the scrubber effluent at the juncture of pipes 18 and 43. This combined stream is then passed through passage 56 of air liquefier 54 and aids in the liquefaction of the air flowing in passage 58. Next the combined stream joins the major portion or flow of the purified scrubber effluent in pipe 48 by means of pipe 81, joining conduit 46 at a point thereof which is between heat exchanger 2! and the secondary compressor 48. In this manner, a united stream is formed which is made up of the major and minor flows from the scrubber 28 and the take-off from the top of the receiver 74. The liquefied air collected in the bottom of the receiver 74 is removed for storage or use through pipe 82. A minor portion is taken from pipe 82 through branch pipe 32 having control valve 85 and is passed to the air scrubber 28 to provide the purified scrubbing liquid which is utilized as previously described.

The valve 42 in conduit 43 is used to vary the quantities of flow of the scrubber effluent via conduits 4'4 and 43 to heat exchanger 2| and air liquefier '54. This division of the air maintains conditions in exchanger 2! and liquefier 54 so that the operating temperature at the warm ends may be adjusted to that temperature which will result in the maximum heat transfer.

The liquefied oxygen or other gas used for liquefying the purified air in liquefier 54 can conveniently be continuously supplied by two containers, so and 92, one or both of which can be a truck trailer tank or a railway tank car. The containers for the liquefied gas are connected by suitably valved conduits 94 and 96 to pipe 98 which leads to passage 50 of air liquefier 54. The liquefied gas supply arrangement is such that the flow of liquefied oxygen to the gasifying passage 66 occurs and would include well-known features such as check valves, safety valves, gravity or pump. feed, and others which are not shown in the interests of clarity.

After being gasified and pressurized in passage 60 of the air liquefier 54, the oxygen gas is directed to welding or other operations which have a rather constant consuming demand by means of pipeline 99.

It is to be noted that the above-described gasifying and pressurizing of the extraneous liquefied oxygen in air liquefier 54 determines the pressure at which the purified air is discharged from secondary compressor 48. For proper distribution of gasified oxygen in welding, cutting, scarfing and other oxygen-consuming operations, it is necessary that the gasified oxygen be pressurized suificiently to be able to pass through the valves and piping of the distribution system and arrive at the point of actual consumption at the proper pressure. Since this pressure is often about 100 p. s. i. g. for pipeline distribution, the purified and compressed air leaving secondary compressor 48 is usually at about 300 p. s. i. g. or less. It is to be noted that the pressure of the compressed air stream (about 300 p. s. i. g.) is about three times higher than the relatively low pressure value of the gasified oxygen (about 100 p. s. i. g.). For some uses of oxygen, a higher pressure is used and hence the heat exchanger and secondary compressor may handle air at somewhat higher but relatively low pressures.

From the foregoing it can be appreciated that a simplified process and apparatus for the purification and liquefaction of air has been provided which efiiciently utilizes the refrigerative capacity of a liquefied gas and at the same time gasifies and pressurizes the extraneous liquefied gas. Since the process and apparatus for the liquefaction of air or other gas is greatly simplified due to external refrigeration by an extraneous liquefied gas, the initial capital investment and the degree of operational control are reduced. Also the process is more readily susceptible to automatic operation. It can be emphasized that, since an extraneous body of liquefied gas constitutes the source of the major refrigeration requirements of the process, the amount of compression, and hence electricity, is greatly reduced and substantial operating economies are possible.

Although the invention has been described with reference to liquefied oxygen, it is to be understood that many other similar gases could be used. Thus, if it were desired to obtain gasified nitrogen, as for purging of certain chemical reactors, nitrogen would be gasified in the process and so furnish refrigeration. Similarly in place of producing liquefied air, the instant invention is adaptable to the production of other liquefied gas mixtures or other gases such as liquid nitrogen. Naturally the liquefied gas and the gas to be liquefied must be compatible in the sense that they must have similar physical characteristics, such as boiling points and latent heats.

Although a preferred embodiment of the invention has been specifically illustrated and described, it will be apparent to one skilled in the art that various changes and modifications might be made without departing from the spirit of the invention as defined in the following claims.

What is claimed is:

1. A process for the production of liquefied air and, simultaneously therewith, the gasification of extraneous liquid oxygen from storage means which comprises compressing an air stream, liquefying the compressed air stream by gasifying 6 and pressurizing a quantity of liquefied oxygen, passing the gasified oxygen towards a point of use which is not associated with said storage means, subcooling the liquefied air stream, expanding the liquefied air so that some vapors are produced, utilizing said vapors in said subcooling of said liquefied air stream and in said liquefying of said compressed air stream, introducing said utlized vapors into said air stream prior to the compression thereof, and collecting and removing said liquefied gas.

2. The process of producing a liquefied air and, simultaneously therewith, gasifying an extraneous stored liquefied gas which comprises compressing an air flow to about 300 p. s. i. g. and removing the heat of compression; liquefying said compressed and cooled air flow by gasifying and pressurizing said extraneous stored liquefied gas whereby said stored liquefied gas is readied for use, passing the gas resulting from the receding step towards a point of use, subcooling said liquefied air flow; expanding said liquefied air fiow and so producing some vapors and residual liquid; recirculating said vapors so that they are used in said subcooling of said liquefied prmary gas stream, then aid in the liquefying of said primary gas stream, and finally join the gas flow prior to the compressing step; and withdrawing the residual liquid.

3. The method of producing liquefied air which comprises the steps of compressing the air to less than 30 p. s. i. g., cooling the compressed air to about its liquefaction temperature, scrubbing and further cooling the cooled compressed air by intimate contact with scrubbed liquefied air thereby removing higher boiling-point impurities, using said scrubbed and further cooled air to effect said first cooling step thereby warming said scrubbed air, compressing said scrubbed and warmed air to the pressure at which it will liquefy when in contact with relatively low pressure evaporating liquid oxygen, liquefying said further compressed air by heat exchange with liquefied oxygen which is thereby evaporated, utilizing a small portion of said liquefied air for said scrubbing and further cooling step, and withdrawing the remainder of said liquefied air.

4. A process for the production of liquefied air which comprises compressing an air stream containing higher boiling point impurities to less than 30 p. s. i. g.; cooling said air stream; purifying and further cooling said air stream by intimately contacting it with purified and liquefied air and thus producing a purified efiluent; dividing said purified efiiuent into a major fraction and a minor fraction; using said major fraction to cool said air stream containing impurities thereby warming said major fraction, warming said minor fraction; uniting said warmed fractions into a combined stream; compressing said combined stream to about 300 p. s. i. g.; converting said combined gaseous stream into its liquid phase by evaporating an extraneous body of liquefied gas; utilizing said minor fraction in said converting step thereby effecting said warming of the minor fraction and so cooling said combined stream; expanding said liquefied combined stream to further cool it and form a quantity of purified liquefied gas; and using a small quantity of the purified liquid gas in said purifying step.

5. A process according to claim 4 wherein the major and minor fractions are so divided as to produce a maximum heat transfer in their respective cooling steps.

6. The method of making a liquefied gas which comprises compressing an incoming gas stream containing higher boiling-point impurities, cooling said incoming stream, scrubbing and further cooling said incoming stream with a purified liquefied gas in order to remove said impurities from said incoming gas stream, dividing said purified incoming gas into a major fiow and a minor flow, warming said major fiow in said cooling step of the incoming gas stream, warming said minor flow, combining said major and minor flows into a combined stream, compressing and cooling said combined stream to form a liquid, using the minor stream in said last mentioned cooling and hence effecting the previously mentioned warming of said minor stream, evaporating a liquefied gas by having it absorb heat in said last mentioned cooling of the combined stream, and using a small portion of the liquid produced to effect said scrubbing.

'7. The method of producing a purified and liquefied gas which comprises compressing and cooling an incoming gas stream, scrubbing and cooling the gas stream with a purified liquefied gas in order to remove impurities from said in- 1 coming gas stream, dividing the efiiuent from said scrubbing step into a minor effluent flow and major efiiuent flow, utilizing said major ef-- fluent stream in said cooling of the incoming gas stream, warming said minor effluent flow, combining said major and minor flow to form a united purified gas stream, compressing said united stream, liquefyin said unit-ed stream by heat exchange with an extraneous body of a liquefied gas and with said minor efiluent fiow thereby effecting the warming thereof, and collecting and removing said liquefied united stream.

8. The method of liquefying and purifying air by utilizing the refrigeration effect of an extraneous liquefied gas which comprises initially compressing and cooling the air, washing the air with previously purified liquid air to provide washed air and liquid air containing impurities, discarding the liquid air containing the impurities, Withdrawing and further compressing the washed air, liquefying the compressed washed air by heat exchange with the extraneous liquefied gas to evaporate the same, and utilizing at least a portion of the liquefied washedair to wash the initially compressed cooled air.

9. The method of liqueiying and purifying air by utilizing the refrigeration effect of an extraneous liquefied gas which comprises compressing the air to a pressure in the neighborhood of 30 pounds per square inch gauge, cooling the compressed air, washing the compressed air with previously purified liquid air to provide washed air and liquid air containing impurities, withdrawing the liquid air containing the impurites, withdrawing and further compressing the washed air, liquefying the compressed washed air by heat exchange with the extraneous liquefied gas whereby the same is evaporated, and utilizing at least a portion of the liquefied washed air to wash the compressed cooled air.

10. Apparatus of the type described comprising the combination of means for compressing and cooling air, a scrubber including means for subjecting compressed air to intimate contact with a liquefied portion thereof to scrub the compressed air, means for supplying the compressed air to the scrubber, means for withdrawing scrubbed air from the scrubber and compressing the same, means for liquefying the compressed scrubbed air by heat exchange with an extraneous liquefied gas, and means for returning a portion of the liquefied scrubbed air to the scrubber to scrub the compressed air supplied thereto.

11. The method of supplying a substantially constant consuming demand for gaseous oxygen, at a relatively low pressure, from a quantity of extraneous liquefied oxygen and simultaneously in cooperation therewith converting air into liquid phase, said method comprising compressing; a stream of said air to a value about three times higher than said relatively low pressure thereby forming a compressed air flow, maintaining a relatively large quantity of said liquefied oxygen which is to be gasified and supplied at said relatively low pressure for said substantially constant demand, passing a stream of said liquefied oxygen in indirect heat exchange with said compressed air flow so that said stream is evaporated and gasified to the extent necessary to be suitable for said demand for gaseous oxygen and so that said compressed air fiow is cooled to substantially its liquefaction temperature, said compressed air flow being such in relation to said stream of liquefied oxygen that the major amount of refrigeration required for liquefying said compressed air fiow is furnished by said stream of liquefied oxygen, and moving said gasified oxygen towards an oxygen consuming operation having said demand.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,920,434 Prescott Aug. 1, 1933 1,976,336 Eichelman Oct. 9, 1934 2,082,189 Twomey June 1, i937 

